Usually, fresh air supply for a room in a building will be provided by air taken from the outside of the building. The amount of relatively course impurities and/or contaminants will be reduced to prevent damage to the air supply system. In one or more further steps the air will be treated in a way to reduce fine impurities to achieve the air quality for the intended use of the rooms in a building.
Typically, such air handling units (AHU) and duct work systems may itself act as a source for impurities of the air provided to a room. These impurities could be caused by production process residues (e.g., oil), contamination during construction and/or deposited impurities during use. All these impurities can additionally cause the growth of organisms which again cause further impurities of the air supplied to the room. Moreover, the air exhausted from a room generally passes a filter or other means for removing impurities as well to prevent contamination of the duct system. One of the causes of air quality problems which even can result in the so-called sick building syndrome are impurities in the air in rooms. The air handling system has therefore generally to be designed, maintained and operated such that impurities from outdoors as well as indoors are appropriately considered. Otherwise, such contaminates could contribute to these air quality problems.
In case of centralised systems the reduction of impurities will be the same for every room in the building, which is practically often not necessary or useful. The purpose of each room can be very different, e.g., in hospitals. Accordingly, such centralised systems will suffer from the disadvantage that the same quality of the incoming air for rooms with different purposes is provided, which means some rooms might not require the air quality provided by the central air handling unit, whereas other rooms might need higher qualities of air than provided by the air handling unit because of its particular purpose.
Thus, systems have been established recently comprising filter units for each room depending on its respective air quality requirements, wherein the incoming air is provided by a central air handling unit. This unit will remove relatively coarse impurities from the air sucked in to avoid damages or clogging of the air distributing system, e.g., pipework, splitting units etc. This pre-filtered air is then distributed to each room and the final cleaning process takes place in each of these rooms. This allows for adapting each of the filter units in a way addressing the specific demand of each room.
Generally, the working principle of air terminal devices is based on the so-called displacement ventilation system, i.e. relatively cool air is introduced into the room preferably at the floor level with a low velocity. By encountering a heat source, e.g., human beings, room equipment etc. the introduced air raises and carries gaseous and partially particulate contamination out of the occupied zone while fresh cooler air is introduced into this zone simultaneously.
A plurality of conventional air terminal devices are known in the art. For example, DE 41 19 503 C2 relates to an apparatus for circulating air into a room. The apparatus comprises a housing with relatively large openings for introducing the air stream into the apparatus and exhausting it therefrom. The openings are covered with perforated plates, a grid or mesh that can be easily removed. Between the back side of the perforated plate, grid or mesh and the respective opening a thin layer dust filter is exchangeably provided. In order to exchange the filter the perforated plate, grid or mesh is removed from the housing and the filter material is exchanged whereupon the apparatus is closed again.
EP 0 838 639 A1 discloses an apparatus for installing a ventilation van preventing dust, gas or the like from coming into a room. The apparatus comprises a L-shaped housing for fixing a ventilation van therein. The housing has an inside opening positioned inside a wall and an outside opening which looks down and is positioned outside the wall. The inside opening is provided with an exhaust filter being able to slide vertically so that it can be removed from the housing. Further, the inside opening is covered with a metallic lid which can be opened or closed. A further filter for absorbed air is provided near the outside opening. Both filters can be exchanged by removing the filter cassette, replacing the filter within the filter cassette with a new one and inserting the filter cassette again into the apparatus.
GB 2 356 359 A discloses an air return register forming part of an air recalculation system. This device comprises a casing, a filter element, a fresh air inlet and air vents. Fresh air is drawn into the casing to the inlet, passes through the filter element and out through the vents. Below the register the fresh air mixes with existing air for recirculation. The air then passes through vents into the casing, through the filter element on the other side of a separating wall and out through outlets which are connected to air distribution units. To replace the filter element, a latch is undone and the bottom frame of the casing is pivoted about a hinge to provide access.
WO 81/01109 A1 discloses a housing for mounting HEPA filters including an open-ended tubular casing and, within the casing, a slide structure for slidably mounting the HEPA filter therein from one of the ends of the casing. A buffer means divides the interior of the casing into respective chambers which, on mounting of the filter in the slide structure, are gas-tightly isolated from each other except by way of the filter and which are accessible for a respective one of the open ends of the casing. Also provided are gas intake/exhaust ports for each of the chambers, a pair of cover members for closing the respective open ends of the casing, each of which cover members includes a flange complementary to the associated end of the casing, and respective clamp and seal means for clamping the cover members to the casing to effect a gas-tight engagement of the flange with the respective ends of the casing.
A further example of an air supply terminal device is described in EP 0 961 088 A2. More precisely, this device is a low-velocity supply air terminal device intended for use in rooms that require an air supply, and comprises an inlet which can be connected to an external supply air duct, an air distributing unit for distributing exiting supply air to the room, and an inner space which is open to the inlet and extends in the longitudinal direction of the device from the inlet to its bottom for transporting and distributing air to the air distributing unit. This space is delimited laterally by an inner air permeable wall of the air distribution unit and, when applicable, also by an outer wall of the device. The device also includes a perforated plate for throttling the flow of supply air. The perforator plate is intended to favour distribution of the supply air vertically and uniformly to the air distribution unit arranged in the form of a distribution plate in the inner space. However, no filter is used in this air terminal device.
Similarly, EP 0 442 856 A1 discloses a supply air terminal device with a casing having a perforated front cover through which air exits into a room and a distribution chamber formed within the casing and intended to receive air from a supply channel. The distribution chamber comprises a wall provided with openings and functioning to release air from the distribution chamber in a divergent flow pattern. The wall is disposed in a direction parallel with the air delivered from the channel and has mutually parallel zones which extend along the direction and which include first zones having openings configured to release air completely rearwards in relation to the flow direction of the air supplied through the channel, and second zones having openings configured to release air substantially perpendicular to this direction. This air terminal device does not comprise a filter.
DE 197 00 340 A1 relates to a filter with a filter frame holding a filter element which is preferably made of an active carbon loaded carrier element. The filter frame is made of a closed cell heat-formable foam material, preferably by vacuum forming. To this end a foam web is initially used to provide a filter frame with an integral bottom or bottom portion that is removed in a second step after the forming process so as to provide a frame in which the filter element can be inserted. Further constructions of filter frames are described, for example, in WO 95/34367 A1, WO 98/20961 A1 and DE 43 08 399 C2.
Furthermore, various vacuum cleaners are known, like e.g. the Dyson™-type vacuum cleaners, that use filter cartridges with HEPA filter materials.
These known filter systems are still not considered satisfactory, particularly for applications with a high demand of protection from impurities, since the exchange of a filter is typically cumbersome and involved with a plurality of handling steps during which typically at least a certain amount of impurities caught by the filter element is released into the environment, thus affecting the overall efficiency of the filter system.
In view of a careful balance of pressure drop and the risk of contaminating the air with already captured impurities in the filters, it is necessary to exchange filters from time to time. Since filters capture contaminants from the air stream which are then stored within a filter medium or media, the pressure drop increases for a specific nominal flow rate after extended usage of the filter. This results in higher power consumption and corresponding costs and eventually may lead to a situation where the ventilation system can not overcome the pressure drop so that the room will no more be provided with fresh air. Furthermore, as already mentioned, there is the risk that the impurities already captured within the filter constitute a potential basis for further impurities of the air, e.g., where they support the growth of micro-organisms. It is therefore important to remove these impurities from the air stream in certain intervals, i.e. the filter needs to be exchanged.
With common high quality filters exchange often takes place only after three to five years in which such secondary impurities may already have been emitted extensively. Accordingly, filter exchange should be done typically in an order of one year or even at shorter intervals depending on the required air quality. However, filter exchange is typically quite cumbersome and involves a plurality of handling steps, and additionally the risk of further contamination by contaminants trapped in the filter element and released during exchange of the filter element.
More precisely, in order to exchange a filter it is typically necessary to open a filter housing or to remove a cover so as to get access to the filter element After having access to the filter element, it is taken out of the filter unit and replaced by a new one. Afterwards, the housing is closed again. During this operation it is likely that impurities and contaminants collected by the filter during its use release from the filter element and contaminate the room. This means that a filter exchange in a sensitive room, e.g., in an intensive care unit, could prevent the room from being further used prior to cleaning and decontamination. This once more needs additional time and involves costs and leads to an extended period within which the room cannot be used. This is particularly true in order to meet the quality standards (hygienic standards) existing for specific rooms.